This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Approximately 500-600 cases of vertical transmission of human immunodeficiency virus type 1 (HIV) now occur annually in the United States. The dramatic reduction in vertical transmission rates in the United States is related to several factors, including: increased provision and acceptance of voluntary counseling and HIV testing of pregnant women, improvements in the medical management of HIV-infected pregnant women, and the development and increased acceptance of interventions to decrease the risk of mother-to-child transmission of HIV.